Electron beam controlling apparatus



Aug. 18, 1959 L. BURNS, JR 2,900,562

ELECTRON BEAM CONTROLLING APPARATUS BY 0m Hmm/fg Allg- 13, 1959' L. 1.,BURNS, .AR 2,900,562

ELEcTRoN BEAM coNTRoLLrNG APPARATUS Filed Jan. .8, 1955 2 Sheets--Sheet2 VVV l +15 Imm/f BY @yd/Lm United States Patent O ELEcrRoN BEAMcoNrRoLLING APPARATUS Leslie L.. Burns, Jr., Princeton, NJ., assgnor toRadio Corporation of America, a corporation of Delaware ApplicationJanuary 18, 1955, Serial No. 482,445

12 Claims. (Cl. 315-18) The present invention relates to noveltelevision imagescanning apparatus and, particularly, to such apparatuswherein a target screen made up of a plurality of areas m ofrespectively different characteristics is scanned by one I' m01' eelectron beams.

Certain forms of color television image-reproducing apparatus, forexample, include a cathode ray tube having a screen made up of aplurality of groups of horizontally disposed strips of elemental sizeand of respectively different component color light emittingcharacteristics and employ one, or more electron beams which scan alongthe strips in a predetermined fashion, parallel thereto, to reproducethe television image. In the case of such arrangements, exactness ofscanning or tracking of the strips by the beam or beams is necessary forproper image rendition. One general form of tracking arrangement is thatwhich provides suitable indicia in the target screen which producetracking index signals in response to electron beam impingement, withthe location of such indicia in relation to strips of predeterminedcharacteristics being preselected in order to give sense or direction tothe index signals thus produced.

One problem which is present in many tracking schemes involving elementswhich provide index signals in response to electron impingement is thatof crosstalk between ythe image-representative video signals and theindex signals. That is, for example, where the intensi-ty or the timingof the index signals is intended to aiford information regarding theextent of tracking deviation or error, it has been found that theintensity of the video signals has an undesirable effect upon the indexsignals lidelity, so that erroneous information as to tracking positionresults.

It is, therefore, a primary object of the present invention to providenovel electron beam tracking means.

Another object of the invention is that of providing means for trackingone or more electron beams in a scanning cathode ray tube, which meansare responsive substantially solely to beam position.

A further object of the invention is the provision of means for trackingone or more electron beams in a scanning tube, which means aresubstantially free of the inuence of extraneous information such asimage content.

In general, the present invention provides, in accordance with anillustrative embodiment, an electron beam tracking arrangement in whichtracking-signal indicia afford signals representative of beam scanningposition in response to electron impingement. Means are provided forelfectively preventing the tracking apparatus from responding toinformation other than that actually representative of beam positioning.In this manner, the tracking function is rendered independent ofirrelevant factors such as image content and the like.

As applied to a color kinescope tracking arrangement, for example, inwhich the relative brightness values of the component colors of theimage have an error-producing effect upon the tracking function, meansare pro- Patented Aug. 18, 1959 ICC vided for unbalancing the trackingcircuits in accordance with the intensity ofthe color or colors likelyto have such effect. Thus, the invention will be understood aseifectively subtracting image signals from the tracking index signals.

Additional objects and advantages of the present invention will becomeapparent to those skilled in the art from a study of the followingdetailed description of the accompanying drawing, in which:

Fig. 1 illustrates, by way of a block and schematic diagram, a colortelevision receiver embodying the principles of the present invention inaccordance with one form thereof;

Fig. 2 illustrates certain wave forms to be described;

Fig. 3 is a schematic diagram of circuitry suitable for use inperforming certain of the functions indicated in Figi. 1 in accordancewith one form of the invention; an

Figs. 4 and 5 are schematic diagrams of additional forms of theinvention.

Referring to the drawing and, particularly, to Fig. 1 thereof, -there isshown an illustrative color television receiver which may be of anysuitable type. An antenna 10 intercepts broadcast signals which may, forexample, be of the presently standardized color television variety andwhich may be viewed as comprising a rst carrier wave which isamplitude-modulated by black and white image information and asub-carrier wave which is phase and amplitude-modulated by informationregarding the hue and saturation of the television subject. Such signalsare applied by the antenna to the receiver section 12 which isrepresented diagrammatically as a block containing the usual RFamplifer, converted, IF amplifier and second detector stages. Thedetected output signals from the receiver section 12 are applied tosuitable color translator circuits 14 which provide simultaneous red,green and blue color representative video signals at the output leads16, 18 and 20. Circuitry suitable for deriving simultaneous red, greenand blue signals from signals standardized by the Federal CommunicationsCommission on December 19, 1953 may be found, for example, in the bookentitled Practical Color Television for the Service Industry, revisededition, April 1954 (second edition, rst printing), published by the RCAService Company Inc.

In the interest of simplicity of presentation, Fig. l illustrates theapparatus 21 for applying such simultaneous signals to the color imagereproducing kinescope 22 as comprising a commutator device having fourstationary sectors 24, 26, 28 and 30 and a rotating contact member 32which successively contacts the stationary sectors. In practice, theapparatus 21 would comprise electronic sampling means. The red, greenand blue signals are applied, respectively, to the sectors 24, 26 and 28and the fourth sector 30 is also provided with the same green videosignals as those applied to the sector 26, for reasons which will becomeapparent. The contact member 32 is electrically connected, by way ofillustration, to the cathode 34 of the kinescope whose control electrode36 is illustrated as connected to a suitable background potential source38. An electrostatic focusing electrode 40 for focusing an electron beam42 produced by the cathode 34 is connected to a suitable positivepotential terminal. A nal anode 44, which may be in the form of aconductive coating on the interior of the kinescope cone portion, isalso provided with a high positive operating potential from the terminal46. A conventional electromagnetic dellection yoke 4S comprisinghorizontal and vertical deflection windings is energized with deflectionsawtooth currents of television line and eld frequencies from scanningcircuits 50 which receive synchronizing pulses derived from the receivedsignals in the Section 12.

The color image reproducing color kinescope 22 also includes a targetscreen 52 which is, by way of illustration, of the horizontal linephosphor strip variety shown more clearly in the enlarged fragmentaryview of Fig. 2. That is, the target screen 52 is made up of a pluralityof triads of phosphor strips, horizontally disposed, with thestripsarranged in the sequence R, G, B, R, G, B. The kinescope is additionallyprovided with an auxiliary deflection coil 54 for producing a highfrequency wobbling of the electron beam, so that the beam is caused totrace a pattern (e.g., sinusoidal) with respect to the phosphor stripsof a triad, such as that indicated in Fig. 2(a) by the dotted line `56.Specifically, -and by way of example, the coil `54 may be energized froma wobble oscillator 57 which provides a color sub-carrier frequency wave(e.g., 3.6 megacycles). The oscillator 57 may be synchronized with thecolor sub-carrier wave by means of the color synchronizing bursts whichoccur during the horizontal blanking intervals of the blanking signalirnmediately following the horizontal scanning synchronizing pulses.Reference may be made to an article entitled The NTSC Color-TVsynchronizing Signal which appeared in the February 1952 issue ofElectronics (Mc- Graw-Hill Publishing Company, Inc.), for a detaileddescription of color synchronizing bursts. While the foregoingdoes notconstitute a part of the present invention, it may be noted brieflythat, since the color information in accordance with present standardsis transmitted as phase and amplitude-modulation of a sub-carrier wave,it is necessary to provide some means for synchronizing the receivercolor decoding or translating circuits with the encoding apparatus ofthe transmitter so that selection of the several color signals may bemade. The bursts, therefore, comprise several cycles of sub-carrier wavefrequency of xed phase, whereby to provide a reference phase for thecolor translating sections of the receiver.

By virtue of the high frequency wobble of the electron beam 42, the beamis caused to traverse the phosphor strips in the sequence R, G, B, G, R,G, B. Since the beam traverses the green phosphor strip twice as oftenas it does each of the other color phosphor strips, the two greencommutator sectors 26 and 30 are provided. With the commutator member 32rotated at the subcarrier rate of 3.6 megacycles (in synchronism withthe wobble frequency), the red, green and blue color video signals arecaused to control the intensity of the beam at the same time that thebeam is on the corresponding phosphor strips of the target 52.

As has been stated, color image reproducing arrangements of the typedescribed normally require means for insuring that the electron beam ofthe kinescope properly tracks the phosphor strips. In accordance withone form of tracking arrangement illustrated herein by way of example,each of the green phosphor strips G is provided with a backing layer 60of a material capable of emitting ultra-violet light in response toelectron impingement. A photocell 62 receives the ultra-'violet lightthrough a window 64 and provides a current in the lead 66 indicative ofthe traversal of the ultra-violet strips 60 by the sinusoidally Wobbledelectron beam. This current is applied to a servo amplifier andassociated tracking control circuits included generally within the block`68, which circuits also receive a reference subcarrier wave from thewobble oscillator `57. The output of the tracking control circuitscomprises, in the usual operation of such arrangements, a signal in thenature of a correction voltage which may be applied to a correction coil70 for causing the electron beam to be repositioned vertically so as totrack the phosphor strips in a desired manner. The correction winding 70may be of any suitable type capable of producing vertical shifting ofthe position of the electron beam 42,

As described thus far, the receiver shown in the drawing is capable ofproducing color images by virtue of the application of color 'videosignals in synchronism with the beam wobble. Such image reproduction,however, depends upon proper beam tracking, as will be appreciated. Inorder that the utility of the present invention as -applied to suchapparatus may be better appreciated, the general operation of one formof tracking control arrangement will be described briey. As will be seenfrom Fig. 2, the electron beam spot 42 travels along a sinusoidal path'56 and, when properly tracking, crosses the ultra-violet index strip 60of a given triad twice during each wobble cycle. The output signal ofthe phototube 62, therefore, during proper tracking will comprise aseries of pulses 74 which are equally spaced in time and which occur attwice the wobble frequency, or at the rate of 7.2 megacycles per second.When the electron beam 42 is erroneously shifted upwardly to an extremeposition so that the negative peaks of the sine wave 56 fall on theultra-violet strip 60, the tracking index signals will occur, as shownin Fig. 2(c), at the rate of 3.6 megacycles per second and phased asshown by the pulses 74. The tracking control circuits 68 derive acorrection signal by comparing the phase of the received pulses with thereference wave from the oscillator 56 and apply the correction voltageto the winding 70 for moving the beam downwardly to its proper position.

Conversely, if the electron beam is erroneously shifted downwardly sothat only the positive peaks of the sine wave 56 strike the ultra-violetlight-emitting index strip 60, the pulses from the phototube 62 will beas indicated by the pulses 74 in Fig. 2(d). The pulses 74" occur at therate of 3.6 megacycles per second and are phased differently (i.e.,displaced) from the pulses 74 which were produced by the beam in itsuppermost erroneous position. In response to the pulses 74, the trackingcontrol circuits produce a correction voltage which, when appliedto thecoil 70, produces upward repositioning of the electron beam 42.

It has been found in connection with beam tracking arrangements of thetype generally described above that the operation of the trackingcontrol circuits is subject to the influence of the content of the videosignals. That is to say, the usual electron distribution of a scanningbeam is of the so-called Gaussian type and the cross sectional area ofsuch a beam increases with beam current. Since beam current is afunction of the intended brightness of a given color in a tube of thetype in question, it will be understood that the cross sectional area ofthe beam varies as the brightness content of the image being reproduced.Moreover, as the intensity of the beam is increased in order toreproduce a bright color, red, for example, the number of peripheral ortail electrons which will undesirably impinge upon the adjacent phosphorstrip also will increase. Translating the foregoing into terms of itseffect upon tracking accuracy, it will be seen that, for example, whenthe image being reproduced constitutes a bright red area, the electronbeam when in the position shown by the spot 42 in Fig. 2(a) will be ofhigh intensity and a portion of the beam electrons will unavoidablyimpinge upon the adjacent ultra-violet lightemitting strip 60. A pulsecorresponding to such impingement upon the ultra-violet strip willappear in the output of the phototube `62 for application to thetracking control circuits y68. Since the tracking control circuitscannot normally distinguish between the pulses produced by actualpassage of the beam across the green phosphor strip G and those producedby fringe electrons from the beam, a correction signal is produced bythe tracking control circuits and applied to the correction winding 70,thereby causing the beam to be shifted upwardly. That is, the pulsesproduced in response to the impingemcnt of the ultra-violet light strip60 by peripheral electrons from the beam when it is reproducing the redinformation cause the tracking control circuits to sense, albeitincorrectly, that the beam is too low, with a resultant undesirableupward repositioning of the beam. The same kind of error, but of theopposite sense, results when the image being reproduced contains abright blue area, in which event peripheral electrons from the beam(when it traverses the blue phosphor strip) impinge upon theultra-violet strip v60 to produce erroneous tracking information. J

The exact manner in which such error may be inadvertently caused by thevideo content of an image being reproduced will be more apparent from aconsideration of the schematic diagram of Fig. 3 which illustrates onespecific form of tracking control arrangement. Current pulses from thephototube 62, such as those shown in wave forms (b), (c) and (d) of Fig.2 are applied to the terminal 66 in Fig. 3. The pulses are amplified bya stage 78 and are limited in amplitude by a limiter circuit 80 prior toapplication to the control grid 82 of a phase-splitter 84. Oppositephases of the pulses produced by the phototube are thus applied via thecapacitors 86 and 88 to the control grids 90 and 92, respectively, ofcomparator tubes 94 and 96 whose cathodes may, as shown, be connected toground potential and whose anodes 98 and 100, respectively, areconnected together at the common load terminal 102 at the upper end ofthe load resistor 104. The suppressor grid 108 of the comparator 94receives a wave of the same phase and frequency as that of the wobblewave applied to the wobble coil 54, while the suppressor grid 106 issupplied with a wave of the opposite polarity (i.e., wobble phase plus180). The control grids 90 and 92 of the comparator tubes are connectedto suitable bias potential terminals 110 and 112, respectively, throughgrid-leak resistors 114 and 116. The common load terminal 102 of thecomparators is connected via a coupling capacitor 118 to the controlelectrode of an output'ampliier 120 which is of conventional form andwhich includes the beam position correction winding 70 in the loadcircuit of its anode 122.

Assuming that the winding 70 which is in circuit with the tube 120 is sooriented with respect to the kinescope 22 that increased current throughthe winding moves the electron beam 42 upwardly, while decreased currentmoves the beam downwardly, the operation of the circuit of Fig. 3 asdescribed thus far will be as follows:

The amplifier 78 may include an even number of stages, so that thepolarity reversal of an amplifier may be disregarded. The output signalof the amplifier 78 will, therefore, be understood as being a signal ofthe same phase as the current produced by the photocell 62 which, aspointed out supra, is illustrated by wave forms (b), (c) and (d) of Fig.2. After passage through the limiter stage 80, the amplied photocellsignal is applied to the comparator `96 and the opposite phase isapplied to the comparator 94, the phase reversal being accomplished inthe phase splitter 84. Assuming that the beam 42 has shifted upwardly sothat the negative peaks of the wobble wave occur on the ultra-violetstrip 60 which is super-imposed on the green phosphor strip, the outputcurrent pulses of the photocell will comprise the pulses 74 which are ofthe opposite phase from the wobble Wave described by the beam. Thecomparator tubes 94 and 96 are so biased that, normally, the currentthrough the winding 70 is sufficient to maintain the beam in a centeredposition. When the input signal to the control grid of the comparator 94is in phase with the wave applied to the suppressor grid 108, however,that tube will conduct more heavily, Ias will the tube 96, causing thevoltage at the terminal 102 to decrease, thereby lowering the potentialof the control grid 120 of the output amplifier 120, with the resultthat current through the winding 70 is decreased in an amount sufficientto move the beam 42 downwardly to its correct position.

Conversely, if the beam erroneously moves downwardly in the scanningprocess, the photocell 62 will produce current pulses 74 (wave form (d)of Fig. 2), with the result that the pulses applied to the control gridsand 92 of the comparator tubes will be substantially of the oppositepolarity from the 3.6 megacycle wave applied to their suppressor grids.Conduction of both of the comparator tubes will, therefore, decrease,causing the potential of the terminal 102 to increase, thereby applyinga more positive potential to the control electrode 10 of the outputamplifier. The current conduction of the amplifier will thus increase tomove the beam 42 upwardly to its proper position.

With the foregoing description in mind, it should be apparent that, forexample, when the image being reproduced is a bright red scene so thatthe intensity of the electron beam 42 while it is traversing the redphosphor strip R is high such that peripheral beam electrons undesirablyimpinge upon the adjacent ultra-violet strip, pulses of current in thephototube will occur at the time of the pulses 74", causing the trackingcontrol circuits to act as though the beam were too low. 0n the otherhand, when a bright blue field is being reproduced, peripheral or fringeelectrons from the beam while it traverses the blue phosphor strip willproduce pulses in the phototube circuit of the phase of pulses 74',tending to cause the tracking circuits to move the beam upwardly. Thepresent invention, therefore, and in ord'er to render the trackingcontrol circuits substantially insensitive to such spurious signals ashave been shown to result from video content, provides means which maybe thought of generally as nnbalancing or counteracting the action ofthe tracking control circuits in accordance with the video content ofthe image being reproduced, so that those l circuits act only onphotocell signals which are truly indicative of beam positioning. VInthe embodiment of Fig. 3, and as indicated generally by the leads 16'and 20' in Fig. l, a version of each of the red and blue video signalsis applied to the tracking control circuits in such manner as to producethe desired unbalancing Specifically, the red and blue video signals areapplied, with sync pulses extending in the positive direction, to thecontrol electrode terminals and 132 of an amplifier 134 and acathode-follower amplifier 136, respectively. The anode load terminal138 of the amplifier 134 is coupled via a capacitor 140 to a point 142on the grid bias resistor 114 of the comparator 94. Similarly, thecathode load terminal 144 of the amplifier 136 is connected via acapacitor 146 to a point 148 on the grid resistor 116 of the comparatortube 96. The amplifiers 134 and 136 are so associated with thecomparator tubes 94 and 96 that conduction of the amplifiers varies thegrid bias potentials applied to the comparator tubes. That is, for thecondition of a bright red elds being reproduced by the kinescope 22,such that the tracking control circuits would otherwise tend erroneouslyto shift the beam upwardly, the negative-going video signal on the gridof the amplifier 134 will cause the potential at the terminal 138 toincrease, thereby rendering the bias on the control electrode 90 lessnegative than the normal bias applied to the terminal 110. Such adecreased negative bias will increase conduction of the comparator tube94, thereby increasing its conductivity. That is, the comparator 94would, in the absence of the control bias applied via the amplifier 134,and in response to spurious photocell signals produced by a bright redspot, tend to decrease the potential of the terminal 102 in order toincrease conduction of the output amplifier 120 to cause upward shiftingof the beam. By virtue of the controlled bias applied to the comparator94 in accordance with the invention, however, that tube conducts moreheavily so that the potential at terminal 102 is decreased with anattendant decrease in conductivity of the output amplifier 120. Theamount by which the conduction of the amplifier 120 is decreased as aresult of the controlled bias applied to the comparator 94 may beadjusted to counteract substantially exactly the undesirable tendency ofthe tracking circuit to shift the beam up when a bright red field isbeing reproduced.

By reason of the cathode follower action of the amplifier 136, thereverse effect is caused to take place in the comparator 96. That is,when the image being reproduced is bright blue, so that the trackingcircuits would otherwise undesirably tend to shift the beam downwardly,the negative-going blue video signal applied to the terminal 132 of thecathode follower 136 will produce a corresponding negative potential atthe terminal 144 which, in turn, will increase the negative bias on theamplifier 96, thereby decreasing conduction in that tube to increase thepositive potential at the terminal 102. Conduction of the outputamplifier 120 is correspondingly increased in an amount sufficient tocounteract the tendency of the tracking circuit to shift the beamdownwardly.

From the foregoing it will be recognized that the embodiment of theinvention shown in Fig. 3 produces unbalancing of the tracking circuitsby varying the control electrode bias of the phase comparator tubeswhich serve to perform the tracking control function. In this manner,the normal tendency of the tracking control circuits to shift the beamup when a bright red field is being produced and to shift the beam downwhen a bright blue field is being produced is substantiallycounteracted. It will further be recognized that control of thecomparator tubes as a function of the red and blue video signals isdictated in the embodiment thus far described by the fact that the redand blue phosphor strips are adjacent to the tracking index signalproducing element or ultraviolet strip 60. Where the tracking indexsignal element is adjacent to color light producing elements other thanred and blue, the video signals representative of such other colorswould be employed in unbalancing the tracking control circuits.

Fig. 4 illustrates another form of the invention as applied to ahorizontal line screen color kinescope of the type shown in Fig. 1. Inthe arrangement of Fig. 4, the comparator tubes 94 and 96' correspond tothe comparators 94 and 96, respectively, of Fig. 3 and the terminal 102'is the same as the load terminal 102 of Fig. 3. Again, as in the case fothe apparatus of Fig. 3, red and blue representative video signals areapplied to the correction apparatus with the sync pulses extending inthe positive direction. Specifically, such video signals are applied tothe input terminals 150 and 152 of a difference amplifier comprising thetubes 154 and 156, connected as shown. The cathodes of the tubes 154 and156 are connected to a common resistor 158, the anode of the tube 154being connected directly to a source of +B potential, while the anode ofthe tube 156 is connected to +B through a load resistor 160 and, via alead 162, to the load terminal 102' of the comparators.

Assuming the same facts as those set forth illustratively in describingthe operation of the apparatus of Fig. 3, when the image beingreproduced is bright red, the video signal applied to the terminal 150will cause the potential at the cathode end of the resistor 158 todecrease in potential, thereby causing a corresponding decrease inpotential at the anode lead 162. Since the lead 162 is connected to theload terminal 102', the conduction of the output amplifier 120"(corresponding to the amplifier 120 of Fig. 3) will be correspondinglydecreased and the amount by which conduction of the amplifier 120" isthus decreased may be adjusted to counteract the amount by which itwould otherwise be caused to increase by the action of the comparatortubes in response to the spurious signals produced in the photocell bythe fringe electrons of the electron beams.

In the case of a bright blue image, the negative-going video signalsapplied to the terminal 152 will cause a decrease in conduction of thetube 156, thereby increasing the potential at its anode. The increasedpositive potential is applied to the load terminal 102 via the lead 162to increase the conductivity of the output amplifier in an amountsufiicient to counteract the decrease in its conductivity which wouldotherwise be brought about by the action of the comparator tubes. Itwill thus be apparent that, in accordance with the form of the inventionshown in Fig. 4, the video signal or image content compensating actiontakes place directly at the control electrode of the output amplifierwhich passes the beam shifting current through the correction coil 70.

Fig. 5 illustrates a further form of the invention by means of whichcompensation for the error-producing effect of image content is broughtabout. In the apparatus of Fig. 5, the compensating or unbalancing ofthe tracking control apparatus is accomplished by supplying a greateramplitude of error signal to the tracking control circuits of one of theerror-indicating phases of photocell signal. That is, as has beenexplained supra, the comparator tubes of the tracking control circuitsshown operate in response to the amplitude and phase of the signalsderived by the phototube. When the photocell Signals are of the phasesho/wn by wave form (c) of Fig. 2 (i.e., pulses 74'), the trackingcircuits tend to decrease the current in the correction winding 70 inorder to shift the beam down. Conversely, pulses of the phase shown inwave form (d) of Fig. 2 cause the comparator tubes to increase thecurrent through the correction winding for a corresponding upward shiftof the electron beam. As has also been pointed out, the normal tendencyof the tracking circuits is that of shifting the beam upwardly when theimage being produced is bright red and shifting the beam downwardly whenthe image is bright blue.

A pair of mixer pentodes 164 and 166 are connected, as shown, with theircathodes joined at a common load terminal 168. The suppressor grid ofthe tube 164 is supplied with a 3.6 megacycle wave of the wobble phase(i.e., corresponding to the phase of the pulses '74" of Fig. 2) whilethe suppressor grid of the tube 166 is supplied with a 3.6 megacyclewave of the opposite polarity. Red and blue video signals ofsync-positive polarity are applied, respectively, to the controlelectrodes and 172 of the tubes 164 and 166. The common load terminal168 is coupled via a capacitor 174 to a point 176 on the grid-leakresistor 178 of an amplifier tube 180 which may, for example, be one ofthe two amplifier stages described in connection with Fig. 3 asfollowing the phototube 62. Thus it will be understood that in Fig. 5,the block 78' is representative of one of the amplifier stages includedin the block 78 of Fig. 3 and that the limiter 80, phase splitter 84,comparators 94 and 96 and output amplifier 120 correspond to the sameelements of the apparatus of Fig. 3.

In *the operation of the form of invention shown in Fig. 5, theconduction of the tubes 164 and 166 is balanced so that substantially noenergy of 3.6 megacycles is present at the terminal 168. When the imagebeing reproduced is bright red, for example, the negativegoing videosignal applied to the control electrode 170 decreased the conductivityof the tube 184 so that there will appear at the terminal 168 a certainamplitude of 3.6 megacycle energy of the opposite polarity from thewobble phase.

In other words, the signal appearing at the terminal 168 and applied viathe capacitor 174 to the control electrode of the amplifier 180 will beof the phase of pulses 74 in Fig. 2 and of sufiicient amplitude as tobalance the effect of the spurious pulses produced in the photocellcircuit by fringe electrons. Thus, the normal tendency of the trackingcontrol circuits to cause a downward shift of the beam during a redfield will be counteracted. On the other hand, when the image producedis bright blue, the negative-going video signal applied to the controlelectrode 172 of the tube 166 will decrease the conductivity of thattube to permit a greater amount of 3.6 megacycle energy of wobble phaseto be 9 applied to the amplifier I180, thereby causing the trackingcircuits to balance out the error which would otherwise result from thevideo content of the television subject.

While the invention has been described in accordance with certainspeciiic embodiments indicated as applicable to a particular form of atracking control arrangement, it will be understood that the principlesof the invention are applicable to other types of tracking controlcircuits in which video compensation is desirable or necessary. Forexample, where an image reproducing kineoscope employs a plurality ofbeams for scanning simultaneously along strip-like elements of a targetscreen, one or more of the beams being modulated by a tag signal usefulin identifying its position as determined by a phototube or the like,the present invention may be employed to counteract the inherenttendency of tracking control circuits (responsive to the amplitude ofsuch a tag signal) to respond erroneously to an increased amplitude ofderived tag information resulting from increased image brightness.

Hence it will be appreciated that the invention nds application inapparatus which includes a tracking arrangement for a plurality of beamcomponents which scan a screen made up of a plurality of areas ofrespectively diierent characteristics and in which the tracking functiondepends upon 'the production of index signals which, in turn, dependupon the intensity of the beam components, regardless of whether thebeam components comprise separate electron beams or a single beam whichtraverses diierent screen areas successively, as illustrated, forexample, on the drawing.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

l. In image reproduction apparatus of the type comprising arcathode raytube having means for causing a plurality of electron beam components toscan across a target screen made up of a plurality of areas ofrespectively different characteristics and tracking indexsignal-producing elements associated with the screen in a xed relationto selected ones of such areas for providing signals in response toelectron impingement indicative of the relative position of at least oneof the beam components with respect to the index elements, means forintensity-modulating such beam components respectively by signalsrepresentative of such respectively different characteristics; trackingcontrol means associated with each tube for receiving such index signalsand operative to correct the position of such beam components inaccordance with such index signals, said index signals being undesirablysubject to spurious eiects from such intensity modulation of said beamcomponents so as to cause said tracking control means to responderroneously to such spurious effects; means for providing a signalproportional to the diierence between the respective intensities of oneof such modulating signals and another of such modulating signals; andmeans coupled to said tracking control means for counteracting theaction of said tracking control means in response to a differencebetween the respective intensities of one of such modulating signals andanother of such modulating signals, such counteraction being in suchdirection as to overcome the erroneous response of said tracking controlmeans.

2.y Image reproduction apparatus comprising: a cathode ray tube havingmeans for causing a plurality of electron beam components to scan acrossa target screen made up of a plurality of areas of respectivelydifferent characteristics and tracking index signal producing elementsassociated with the screen in a fixed relation to selected ones of suchareas for providing signals in response to electron impingementindicative of the relative position of at least one of the beamcomponents with respect to the index elements, and means for intensitymodulating such beam components respectively with signals representativeof such respectively different characteristics, tracking control meansassociated with such tube for receiving such index signals and operativeto correct the position of such beam components in accordance with suchindex signals, said index signals being undesirably subject to spuriouseffects from such intensity modulation of said beam components so as tocause said tracking control means to respond erroneously to suchspurious effects; means for providing a signal proportional to thedifference between the respective intensities of one of such modulatingsignals and another of such modulating signals; and means coupled tosaid tracking control means and to said modulating means forcounteracting the action of said tracking control means in response to adiierence between the respective intensities of one of such modulatingsignals and another of such modulating signals, such counteraction beingin such direction as to overcome the erroneous response of said trackingcontrol means.

3. In image reproduction apparatus of the type comprising a cathode raytube having means for causing a plurality of electron beam components toscan across a target screen made up of a plurality of areas ofrespectively different characteristics and tracking indexsignal-producing elements associated with the screen in a fixed relationt0 selected ones of such areas for providing signals in response toelectron impingement indicative of the relative position of at least oneof the beam components with respect to the index elements; means forintensity-modulating such beam components respectively with signalsrepresentative of such respectively diEerent characteristics such thatsuch index signals are inherently subject to spurious effects resultingfrom the intensity of such modulating signals, tracking control meansassociated with such tube for receiving such index signals and operativeto correct the position of such beam components in accordance with theintensity of such index signals, said tracking control means beingundesirably responsive to such spurious eiects; means for providing asignal proportional to the difference in intensity between selected onesof such modulating signals; and means coupled to said tracking controlmeans and to said last named means for controlling the action of saidtracking control means in response to and in accordance with adifference between the respective intensities of one of such modulatingsignals and another of such modulating signals, thereby to overcome theundesired response of said tracking control means to such spuriouselects.

4. In image reproduction apparatus of the type comprising a cathode raytube having means for causing a plurality of electron beam components toscan across a target screen made up of a plurality of areas ofrespectively diierent characteristics and tracking indexsignal-producing elements. associated with the screen in a iixedrelation to selected ones of such areas for providing signals inresponse to electron impingement indicative of the relative position ofat least one of the beam components with respectl to the index element,tracking control means associated with such tube for detecting errorsignals from said index signals and operative to shift the position ofsuch beam components in a direction tending to correct the position ofsuch beam components and in accordance with the intensity of such errorsignals, means for modulating such beam components respectively inintensity by signals representative of such respectively differentcharacteristics such that spurious index signals are produced when oneof such beam components is modulated by high-intensity signals so thatsaid control means responds erroneously to said error signals to movesaid beam components in an amount proportional to the intensity of suchmodulation; means for producing a compensating signal proportional tothe intensity of such modulation; and means coupled to said trackcontrol means and to said compensating signal producing means forcounteracting the action of said tracking control means as a function ofthe intensity of one of such modulating signals, such counteractionbeing in the direction of overcoming the erroneous response of saidtracking control means.

5. In image reproduction apparatus of the type comprising a cathode raytube having means for causing a plurality of electron beam components toscan across a target screen made up of a plurality of areas ofrespectively different characteristics and tracking indexsignal-producing elements associated with the screen in a fixed relationto selected ones of such areas for providing signals in response toelectron impingement indicative of the relative position of at least oneof the beam components with respect to the index elements, correctionmeans associated with such tube for identifying such index signals andoperative to shift the position of such beam components in the directionof correcting the position of such beam components and in accordancewith such index signals, means for modulating such beam componentsrespectively in intensity by signals of such respectively differentcharacteristics such that spurious index signals are produced when oneof such beam components is modulated by high-intensity signals, saidcorrection means being undesirably responsive to such spurious indexsignals; means coupled to said modulating means for producing acompensating signal proportional to the intensity of one of suchmodulating signals; and means coupled to said correction means forcounteracting the action of said correction means as a function of theintensity of one of such modulating signals, such counteraction being inthe direction of overcoming the undesirable response of said correctionmeans to such spurious index signals.

6. Color image reproduction apparatus comprising a cathode ray tubehaving means for causing a plurality of electron beam components to scanacross a target screen made up of a plurality of areas of respectivelydifferent color characteristics and tracking index signal producingelements associated with the screen in a fixed relation to selected onesof such areas for providing signals indicative of the relative positionof at least one of the beam components with respect to the indexelements, means for intensity modulating such beam components by signalsrepresentative of such respectively different color characteristics,said index signals being undesirably subject to spurious effects fromsuch intensity modulation of said beam components; tracking correctionmeans associated with such tube for receiving such index signals andoperative to shift the position of such beam components in the directionof correcting the position of such beam components and in accordancewith such index signals, said tracking correction means beingundesirably responsive to said spurious effects such as to cause anerroneous shift of the position of said beam components, means coupledto said modulating means for producing a compensating signal whichvaries as a function of the intensity of at least one of such modulatingsignals, and means coupled to said tracking correction means and to saidlast-named means for counteracting the action of said trackingcorrection means as a function of the intensity of at least one of suchmodulating signals, such counteraction being in the direction ofovercoming the undesirable response of said correction means to suchspurious effects.

7. The invention as defined by claim 6 wherein said means for causing aplurality of electron beam components to scan said target screencomprises a source of a single electron beam and deflection meansassociated with said tube for causing said beam to undulate verticallyas it scans and in such manner as to impinge successively, during suchundulation, upon said areas of different color characteristics and atleast one index element.

8. Image reproduction apparatus comprising a cathode ray tube havingmeans for causing a plurality of electron beam components to scan acrossa target screen made up of a plurality of areas of respectivelydifferent characteristics and tracking index signal producing elementsassociated with the screen in a fixed relation to selected 'ones of suchareas for providing signals indicative of the relative position of atleast one of the beam components with respect to the index elements,means for intensity modulating such beam components by signalsrepresentative of such respectively different characteristics; trackingcontrol means associated with such tube for receiving such index signalsand operative to correct the position of such beam components inaccordance with such index signals, said index signals being undesirablysubject to spurious effects from such intensity modulation of said beamcomponents such as to cause said tracking control means to responderroneously to such spurious effects; means coupled to said modulatingmeans for providing a compensating signal which varies as a function ofthe intensity of at least one of such modulating signals, and meanscoupled to said tracking control means for counteracting the action ofsaid tracking control means as a function of the intensity of at leastone of such modulating signals, such counteraction being in thedirection of overcoming the erroneous response of said tracking controlmeans.

9. The invention as defined by claim 8 wherein said means for causing aplurality of electron beam components to scan said target screencomprises a source of a single electron beam and deflection meansassociated with said tube for causing said beam to undulate verticallyas it scans and in such manner as to impinge successively, during suchundulation, upon said areas of different color characteristics and atleast one index element.

10. Image reproduction apparatus comprising a cathode ray tube having atarget screen made up of a plurality of groups of horizontally orientedstrip-like elements, each group including at least first and secondstrip-like elements of respectively different characteristics and meansfor causing a plurality of electron beam components to scan across saidscreen horizontally, there being a beam component for each of said firstand second striplike elements of a group; means responsive to theimpingement of one of such beam components upon such first strip-likeelement of a group for producing a tracking index signal; trackingcorrection means associated with said last-named means for identifyingsuch index signals and shifting the vertical position of such beamcomponents vertically in the direction indicated by said index signalsand in an amount which is a function of the intensity of such indexsignals; means coupled to said cathode ray tube for intensity modulatingsaid beam components with signals representative of such respectivelydiierent characteristics, said index signals being undesirably subjectto spurious inuence by such intensity modulation of said beamcomponents; and means coupled to said modulating means and to saidtracking correction means for applying signals from said modulatingmeans to said tracking correction means to control the action of saidtracking correction means as a measure of the intensity of the signalmodulating the beam component which impinges upon such second strip-likeelement of the same group and in such manner as to compensate for thespurious influence of said beam component intensity modulation upon saidindex signals.

l1. Image reproduction apparatus comprising a cathode ray tube having atarget screen made up of a plurality of groups of horizontally orientedstrip-like elements, each group including at least first and secondstrip-like elements of respectively different characteristics and meansfor causing a plurality of electron beam components to scan across saidscreen horizontally, there being a beam component for each strip-likeelement of a group; and index signal producing element associated withsaid first strip-like elements of a group for producing a tracking indexsignal in response to electron impingement;

correction means associated with said last-named means for identifyingsuch index signals and shifting the vertical position of such beamcomponents as a function of the intensity of such index signals; meanscoupled to said cathode ray tube for intensity modulating said beamcomponents with signals representative of such respectively dierentcharacteristics; said index signals being undesirably subject tospurious effects from such intensity modulation of said beam componentsso as to eause said correction means to respond erroneously to suchspurious effects; means for providing a signal proportional to theintensity of the signal modulating that beam component which impingesupon such second strip-like element of the same group and means coupledto said last-named means and to said correction means for applyingsignals from said last-named means to said correction means to controlthe action of said correction means as a measure of the intensity of thesignal modulating the beam component which impinges upon such secondstrip-like element of the same group, thereby to overcome the erroneousresponse of said correction means to said spurious effects.

12. Image reproduction apparatus comprising a cathode ray tube having atarget screen made up of a plurality of groups of horizontally orientedstrip-like elements, each group including at least rst, second and thirdstriplike elements of respectively dierent characteristics arranged oneabove the other and means for causing a plurality of electron beamcomponents to scan across said screen horizontally, there being a beamcomponent for each strip-like element of a group; means responsive tothe impingement of electrons upon such second striplike elements of agroup for producing a tracking index signal; correction means associatedwith said last-named means for identifying such index signals andshifting the vertical position of such beam components as a function ofsuch index signals; means coupled to said cathode ray tube for intensitymodulating said beam components with signals representative of suchrespectively diterent characteristics, said index signals beingundesirably subject to spurious effects from such intensity modulationof said beam components so as to cause said correction means to responderroneously to such spurious effects; and means coupled to saidmodulating means for producing a compensating signal which is a measureof the intensities of the signals modulating the beam components whichimpinge, respectively, upon said first and third strip-like elements ofthe same group; and means coupled to said last-named means and to saidcorrection means for applying said compensating signal to saidcorrection means thereby to overcome such erroneous response of saidcorrection means.

References Cited in the tile of this patent UNITED STATES PATENTS2,490,812 Human Dec. 13, 1949 2,530,431 Huffman Nov. 21, 1950 2,664,520Wiens Dec. 29, 1953 2,706,216 Lesti Apr. 12, 1955 2,777,087 Fromm Jan.8, 1957

